Dispersed particles such as vinyl plastisol resins desirably have a high plasticizer capacity, an increased flexibility, workability, and distensibility. Usually, these resins are made by an emulsion polymerization process in which relatively large quantities of emulsifiers or soaps are utilized. In emulsion polymerization, the finished product is a polymer latex, which, theoretically, can be coagulated, filtered to remove the polymer particles and then dried. However, it is difficult to conduct such a process without forming agglomerates of polymer which cannot be disintegrated without using harsh grinding procedures which often adversely affect the quality of the polymer. If the resin is used as is, the agglomerates are excessively large and detract from the usefulness of the resin when vinyl resin plastisols are subsequently made. The use of coagulation aids is also necessary and often imparts undesirable properties to the resin. As a result, it has been the common practice in the industry to take the polymer latex having polymer particles of the proper predetermined size and spray-dry the latex. However, a drawback of this procedure is that all of the emulsifier or soap, initially added to the polymerization mixture, is deposited on the polymer particles. Various properties of products made from the particles can be affected, for example, clarity and gloss. Also, the large amount of soap present can adversely affect the viscosity of a plastisol. The color of the final product may be affected by the soap since the same may discolor at processing temperatures. An additional drawback of the spray drying method is that large amounts of energy are required to remove the water by evaporation.
While many attempts have been made to remove the soap from vinyl dispersion resins by simple washing, most have run into various kinds of technical problems. Also, the various proposals have been expensive and complicated. As a result, little has been done to remove the soap after the spray-drying operation.
U.S. Pat. No. 3,901,842 relates to coagulation of a vinyl polymer latex, centrifuging the same to form a polymer wetcake and then redispersing the wetcake by use of a redispersant such as a polyacrylate. Thereafter the redispersed wetcake is dried in a spray-dryer.
U.S. Pat. No. 4,292,424 to Huddleston et al relates to the production of vinyl dispersion resins by means of emulsion polymerization and the recovery of the resins by a process which includes coagulating the latex to form a filtering sludge, passing the sludge to a pressure filter to separate the high solids, forming a friable wetcake, rinsing the wetcake with proper agents to neutralize the same and removing undesirable residues. Pressure in the filter is applied to the rinsed wetcake to increase the solids content thereof. The wetcake is then broken into particles and dried and ground to a proper size in one step in a fluid energy mill.
U.S. Pat. No. 4,207,158 relates to a process for dewatering a suspension of solids utilizing an electrically augmented vacuum filtration apparatus.
U.S. Pat. No. 4,331,525 relates to a process and apparatus for the recovery of suspended solids from a liquid medium. The liquid medium containing suspended solids is circulated through an electrolytic cell and an ultrafiltration unit, the suspended solids being removed from the liquid medium as a uniform particulate mass of low liquid content while a proportionate amount of the liquid and dissolved components such as surfactants is removed through ultrafiltration to avoid a dilution of the liquid medium.
European Patent Application No. 0,028,837 relates to a processing apparatus for recovering suspended solids from a liquid medium. An electrolytic cell as well as an ultrafiltration unit is utilized.
U.S. Pat. No. 4,134,820 relates to an apparatus for removing a wetcake from an anode in an electrofiltration process.
U.S. Pat. No. 4,107,026 relates to a method and apparatus for dewatering suspended matter and includes the use of vacuum filtration.
U.S. Pat. No. 4,246,039 is similar to U.S. Pat. No. 4,107,026 and also relates to the use of electrofilitration.